1. Field of the Invention
The present invention relates to a pulley unit to be mounted in an auxiliary device, which is a device driven by a belt combined with a crank shaft of an engine of a vehicle, for example. Examples of such an auxiliary device are a compressor for an air conditioner, a water pump, an alternator, and a cooling fan of a vehicle, for example.
2. Description of the Related Art
An example of such a pulley unit in the prior art is shown in FIGS. 8 and 9. In those figures, reference numerals 81, 82, 83 and 84 denote, respectively, a pulley, a shaft, a one-way clutch and a rolling bearing. The one-way clutch 83 has an inner ring 85, an outer ring 86, a plurality of rollers 87, cage 88 and a coil spring 89.
When the cage 88 in such a one-way clutch 83 jolts in the angular and/or axial direction with respect to the inner ring 85, the functions of the locking in and the releasing free of the one-way clutch 83 tend to be unstable. Therefore, two radially inward directed projections 90, 90 having different angular positions are provided on one of the shaft ends of the cage 88, and two slits 91, 91 having different angular positions are provided on one of the ends of the inner ring 85; the projections 90, 90 and the slits 91, 91 are engaged with each other in the axial direction thereof so that the cage 88 is positioned exactly at a predetermined position in the angular direction and in the axial direction with respect to the inner ring 85 in order to prevent such instability.
There is room for improvement in the positioning of the cage 88 in the one-way clutch 83 in the prior art.
In the prior art, the inner ring 85 is forced fit around the shaft 82 by force so that the rotation around the shaft is prevented. However the forced fitting causes a stress acting to the inner ring 85 in the angular direction. The stress tends to concentrates to the inner corner of the slits 91, 91 of the inner ring 85. Thus there is danger of cracking of the inner ring 85 starting from the stress concentrated point.
Other problems are the low efficiency of the working to form the slits 91, 91, and the necessity of the treatment afterward for removing burr. Therefore the fabrication cost is expensive.